Electric heater



March 27, 1928.

S. MORSE ELECTRIC HEATER Filed Feb. 6, 1926/ 2 Sweater-Sheet 1 n Ha.

l Sterne MOT-5e zu GMJ 2n March 27, 1928.

1,663,810 s. MORSE ELECTRIC HEATER Filed Feb. 6. 1926 2 Sheets-Sheen te rne MOYSe Patented Mar. 27, 1928.

UNITED STATES PATENT OFFICE.

STERNE MORSE, 0F CLEVELAND HEIGHTS, OHIO.

ELECTRIC HEATER.

Application filed February This invention relates to electric heating units, and particularly to an electric heater unit adapted to maintain itself automatically at substantially constant temperatures.

Electric heating units have become very desirable for domestic use in connection with household cook stoves, ovens and also for commercial and scientific use in various forms of heaters, furnaces, ovens, etc. To make such heating units commercially practicable and to adapt them to wide use, it is desirable that the heater be of cheap, economical and rugged construction. It is also very desirable that such heating units be adapted to maintain the heated device at substantially constant temperatures. Substantially constant temperatures in the heated device have heretofore been obtained by the. use of suitable supplemental thermostat control units.

Resistors embodying a series of contacting carbon blocks, commonly referred to as carbon pile resistors, have been previously proposed for various purposes other than heating. For example, carbon pile resistors have been proposed heretofore in which the inherent negative coetlicient of resistance of the carbon unit was compensated for sufficiently to provide a resistor having substantially no change in its resistance over a relatively wide operating range.

This invention differs fundan'ientally from the above mentioned types of resistors in that a heating unit is herein proposed, which unit automatically maintains itself at substantially constant temperatures. This insures a substantially constant temperature in the heated medium without the use 0f supplemental thermostat devices. This result is obtained by providing a heating unit which as a Whole has a much larger positive temperature coefficient of resistance than that of any known metallic resistor. Moreover, the resistor portions of a heating unit embodying my invention have a relatively large heat transmitting surface and are ordinarily in heat conducting relation with the object or body to be heated, whereby the heating unit: may be operated at temperatures relatively close to that of said heated body. Owing to the very high temperature coefficient of resistance thereof, the resistance of the complete unit increases very rapidly with slight increases in its temperature, thus automatically reducing the energy input to the resistor when the operating 6, 1926. Serial No. 86,413.

temperature of the heating unit increases but slightly. The heating element herein proposed may, therefore, be said to inherently maintain itself at a substantially constant operating temperature as distinguished from previously proposed heating units which operate at materially higher temperatures than the medium being heated and which attempt to maintain a substantially uniform temperature in the heated body through changes in the electric current traversing the resistor effected by the operation of thermostatic devices.

An object of this invention is to provide a self-controlling electric heating unit having a very high positive temperature coetlicient of resistance, whereby the temperature of said unit may be maintained substantially constant within very narrow limits.

A further object of the invention is to provide a heating unit, the resistor portions of which may be maintained at temperatures but slightly greater than that of the object to be heated, whereby ruggedncss and longevity of the heating unit may be readily obtained.

Another object of my invention is to provide a heating unit adapted to maintain itself within very close limits at predetermined adjusted temperatures.

A. further object of this invention is to provide an electrical heating unit comprising a multi-part resistor of relatively small temperature coetlicient of expansion cooperating with a material of relatively high temperature coefiicientof expansion so arranged that the heating unit as a whole will have a relatively high positive temperature coeliicient of resistance.

A further object of the invention is to provide an electrical heating unit which will very rapidly heat up to a predetermined desired operating temperature.

Another object of this invention is to provide an electrical heating unit of simple, rugged and economical construction for use in cook stoves, ovens and other heating devices.

Other obje-cts of the invention will be apparent to those skilled in the art from the description of it hereinafter given.

ln the accompanying drawings:

Figure l is a horizontal longitudinal section of a heating unit in which aligned resistor blocks or bodies are disposed Within a container;

lll)

Fig. 2 is a vertical longitudinal section of the heating unit shown in Fig. 1;

Fig. 3 is a longitudinal section of' a heating unit in which resistor blocks are disposed within a closed tube;

Fig. 4 is sectional view Fig. 3;

Fig. 5 is a longitudinal section of a Jform ot heating unit in which resistor particles or bodies are `disposed Within a closed container;

Fig. 6 is a sectional view on line G-G of Fig. 5;

Fig. Gn is an enlarged sectional View of the pressure applying means and adjacent portions shown in Figs. 1, 2, 3 and 5;

Fig. 'i' is a longitudinal section of another form of heating unit in which apertured resistor blocks are mounted on a rod;

Fig. 8 is a sectional view on line 8-8 of Fig. 7;

Fig. 9 is a sectional view on line 99 ot Fig. 1() showing a heater in which resistor blocks are disposed within a circular container and adjacent to the walls thereof;

Fig. 10 is a vertical section on line 10-10 of Fig. 9;

Fig. 11 is a plan view ot a heating unit in which resistor blocks and a cooperating member are arranged in spiral form;

Fig. 12 is an elevation, partly in section, on line 12-12 of Fig. 11;

Fig. 13 is a horizontal section of a heating unit in which resistor blocks are arranged in aligned relation within a spiral tube;

Fig. 14 is a vertical section on line 141-1-l of Fig. 13;

Fig. 15 is a plan view of another form of heating unit in which resistor' blocks and a cooperating member are arranged in spiralv form;

Fig. 16 is an elevation, partly in section, on line 16 16 ot' Fig. 15;

Fig. 17 is a plan view, partly in section; of a orm of heating unit in which resistor blocks are arranged in aligned relation within a spiral cavity formed between two cooperating members;

Fig. 18 is a vertical section on line 18H18 of Fig. 17;

Fig. 19 is a plan View, partly in section. of a form of heating unit in which apertured resistor blocks are mounted on a spiral rod;

Fig. 20 is a sectional view on line 20-20 of Fig. 19;

Fig. 21 is an enlarged view of a 'form of resistor block or body;

Fig. 22 is an enlarged view of another form of resistor block;

Fig. 23 is an enlarged View of a rectangular resistor block;

Fig. 24 is an enlarged view ot a resistor block having cylindrical convex ends;

Fig. 25 is an enlarged View of a resistor on line 4 4 of block having one cylindrical concave and one cylindrical convex end;

Fig. 26 is an enlarged view of an apertured spherical resistor block;

Fig. 27 is an enlarged view of a cylindrical resist-or block having one spherical concave, and one spherical convex end;

Fig. 28 is an enlarged view ot a cylindrical resistor block having spherical convex ends;

Fig. 29 is a view showing various forms of resistor particles for use in a form of heating unit similar to that shown in Figs. 5 and 6; and

Fig. 30 is an enlarged sectional view of a resistor block provided with an electrical insulating shell.

One form ot heating unit contemplated by my invention may comprise a series of substantially contacting aligned resistor blocks or bodies disposed adjacent to a conlining or cooperating or expansion member adapted to receive heat from said blocks. Said cooperating member preferably has a relatively high temperature coetlicient oi eXpansion with respect to that ot' said blocks, and if electrically conductive; is insulated from said blocks. Electric connections are provided whereby electric energy, preferably at constant voltage, may be passed through said aligned blocks. It may be noted that ordinarily a large proportion of the electric resistance of said series of blocks is due to the contact resistance between adjacent blocks.

Adjustable pressure applying means is provided whereby said blocks may be placed under an adjustable predetermined initial longitudinal pressure. Said pressure applying means cooperates with said cooperating member so that the pressure between the resistor portions will be decreased on expansion of said cooperating member, due to heat received from said resistor' blocks, and vice versa. The temperature at which the heating unit ismaintained is dependent upon the initial pressure placed upon said blocks by said pressure applying means. ln a heating unit as above described, it will be seen that when the series of blocks has substantially attained the desired temperature. a slight further increase in temperature will` cause reduction of the mutual pressure between said blocks and hence considerably increase the resistance of the entire series of blocks. rlhus l have provided a heating unit which, due to its high temperature coefficient ot resistance, is adapted to maintain itself at predetermined temperatures within very close limits.

It may be further mentioned that, on account of the extent and character of Contact between the series of resistor blocks and. the body to be heated, the temperature ot' said resistor blocks may be but slightly higher llo than that of the heated object, thereby increasing to a very appreciable degree the lite ol:l the heating unit and rendering possible a thermostatie control based in part on the ten'iperature ot the resistor.

In Figs. l and 2 is shown one forni et heating unit contemplated by my invention, comprising a container l, which may be ot metal and which preferably has a. high temperature coel'licient of expansion. Disposed within said container l is a series of substantially contacting aligned resistor blocks or bodies 2, which may be composed of any suitable resistor material, such as, for eX- ample, compressed graphite. The container l is adapted to receive heat from the resistor` blocks when said blocks 2 are heated, and is electrically insulated therefrom by suitable insulating means 3, such as vitreous enamel, mica, etc. Electric energy may be supplied to said blocks 2 through conductors #l and 5, which, in turn, are shown as contacting electrically with the conducting blocks 6 and 7, the electric energy being transmitted through the series of blocks 2 between the conducting blocks 6 and 7. The blocks 6 and 7 assist also in applying pressure to said blocks 2. As will be more readily seen by reference to Fig. (3, a threaded spindle 8 is adapted to move through the threaded boss 9. One end ot' said spindle S is operatively connected to the block 7 and insulated therefrom and the other end of the spindle 8 is shown as provided with a knurled head l0. Thus by turning the head l() the resistor blocks 2 may be compressed between the blocks 6 and 7 to any desired degree. The higher the operating temperature of the heating unit desired, the greater is the initial longitudinal pressure imposed upon said blocks 2.

ln Figs. 3 and fl is shown a heating unit comprising a closed tube 1l in which disposed a series ot' substantially contacting aligned circular resistor blocks 12. The end 13 may be suitably atlixed to the tube ll by any suitable means, as by welding. rlhe electric conducting blocks ld and l5 are preferably similar in cross section to resistor blocks l2, and are similar in construction and function to the blocks 6 and 7 of Fig. l. linsulating means 3, conductors e and 5, spindle 8, boss 9 and knurled head l0 are similar in construction and tune-tion to the corresponding members described under Figs. l and 2.

In Figs. 7 and 8 is shown anothn form ot heating unit in which series ol apertured resistor blocks 1G is disposed on a rod 17, which is provided with an enlarged portion 18 at one end and a threaded portion i9 at the other end. Conductors 2() and 2l are connected respectively to blocks 22 and 2S, whereby electric energy may be readily supplied tothe blocks 16. Electric insulation 2e is disposed between the rod 17 and blocks 1G, 22 and between the enlarged portion 18 and block 22, and between blocl 23 and member 2G. Pressure may be imposed upon the resistor blocks 16 by turning the nut 25, whereby the pressure is transmitted through the member 2G and block 23 to the resistor blocks 1G.

Heaters embodying my invention and arranged in spiral form are advantageous for many purposes since thereby a relatively large heating surface can be arranged in a small space. rllhus such heating units might be advantageously employed in domestic stoves for hot plates. ln Figs. 13 and lli is shown a spiral tubular form of heater which, except for its spiral shape, is quite similar in its general characteristics to the herding unit shown in Figs, t3 and 4. Tvvithn the s `nial tube 27, which is preferably o metal, are shown a series of spirally aligned resistor' blocks 28. '.lhe blocks as shown are o'l substantially cylindrical shape with spherically convex ends, whereby the blocks 28 may readily contact one with another, regardless of the curvature of the spiral. rlhe blocks 28 are suitably insulated from the metal tube 27 by any suitable insulating means 29. At the inner end of the spiral is shown an electric conductor El() connected to a liXed conducting block 3l, which block 3l is insulated from the tube 27 and against which one of the resistor blocks 28 abuts. At the outer end of the spiral an electric conduc-tor 32 is connected to aconducting block 33 lixedly disposed adjacent the outer end of the spiral 27 but insulated therefrom. illovable through the block 33 is the threaded spindle 34 having a lmurled head 35 and provided at its inner end with an enlarged portion 3G. By suitably turning the head 35, the resistor' blocks 2S may be placed under a predetern'iined pressure between the movable portion. 36 and the stationary block 8l. A spiral heater contemplated by my invention may be disposed entirely in one plane as shown in Figs. 13 and lfl; or may be disposed in a plurality of planes as in tbe case oli a spiral ascending about a cyliinlrical space.

ln Figs. Yi7 and t8 is shown another 'term of spiral heater in which a spiral tubular cavity is formed between the cotnperating metal members 37 and which incn'ibers may be suitably afliized in coo; erative rela tion, as by welding. lVithin the cavity are shown the spirally aligned rcs.tor bloclts 39, which in this case are shown as cylin drical in shape, one end of which being spherically concave and the other end spherv ically convex, whereby the blocks 3S) may readily contact one with another. regardless of the curvature of the spiral. it:etween the resistor blocks 39 and the members 37 and 38 is disposed suitable electric insulating` means (not shown). .at the inner end of the spiral is the electric conductor Ill, connected to the conductive block 43, which is disposed at the inner end ot the spiral cavity and which is also suitably electrically insulated 'from the portions 37 and 38. At the outer end ot the spiral is the electric conductor 43 attached to the conductive block del, which block is iixedly mounted at the outer end oir' the spiral cavity and insulated trom the sides thereof. Movable through the block le is the threaded spindle l5 provided with a knurled head 4G and connected at the inner end thereof by a suitable joint with the member 45T through which pressure may be exerted upon the series of resistor blocks 39.

n Figs. 19 and 2O is shown a 'form oi heating unit somewhat similar to that shown in Figs. 7 and 8 but spiral in `forni. Gn the spiral. rod i8 is disposed a series oit spirally aligned apertured resistor blocl-:s if). The blocks 49 are shown as being substantially spherical in shape. rhe rod 48 is provided with a suitable insulating` coating 50. At the inner end of this spiral is an electric conductor 5l connected with a comlucting` block 52 held in position by the enlarged end of the rod 48 and insulated trom said rod 48 and said end One et the resistor blocks 49 abuts the block o2. At the outer end et the spiral is an electric conductor 54 which is connected to a conducting block 55. On the outer threaded end otl the rod 48 is a knurled nut 5G, which is adapted to more the block 55 to thereby place the series ol resistor blocks 49 under a predetermined pressure.

ln 9 and l0 a circular form ot heater is shown in which a series of circularly aligned resistor blocks 57 shown as di-sposed within a circular container 58 and adjacent to and closely following the curvature ot the inner or concave wall thereoilz. lllectric insulating means 60 is disposed intermediate the blocks 57 and container 5S. Adjacent to one end ot said series o'l blocks is an electric conductor 6l connected to a suitable binding post which, in turn. supports a conducting` block 63 in tiXed relation adjacent to one end ot said series ot blocks. Adjacent to the other end ot' said series is a conductor tl; connected to a landing post titi, which supports in tired relation a conducting bloei; 66. Movable through the block G6 i-s a threaded spindle 6T provided at one end with a lmurled head 68. rlfhe other end oil said spindle 67 is connected through a suitable joint to a block 69 adjacent to the other end of the series ot resistor blocks. By turning the head 68 any predetermined longitudinal pressure may be imposed on the series of resistor blocks 5f?.

lt will be noted that in this construction a component of the pressure exerted longitudinally on the blocks 57 presses said blocks radially against the inner concave wall of the container 58 with a torce proportional to the said longitudinal pressure, whereby transmission of heat 'from said blocks to said container 58 is facilitated and whereby the blocks are caused to retain the desired aligned position. lt will be observed, ot course, that a curvature ot relatively large radius is suliicient to obtain the above mentioned desirable characteristics. The conductivity ot the heat from said blocks to said container is. ot' course, substantially in proportion to the heat produced by said blocks, so that the temperature difference between the blocks and the container may remain substantially constant regardless of the amount of heat produced.

To illustrate the operation ot my invention, a heating unit similar to that shown in 9 and i() was operated continuously for about live weeks at definite predetermined temperatures throughout a range trom 35 to 275 degrees centigrade. rIhe resistor blocks employed were ot graphite and were sul'- stantially rectangular in shape, the width of each block between junctions being approximately it, At temperatures of about 100O C. the temperature ot1 the heater was maintained constant within 2 tor periods et several hours. At this temperature the voltage drop across each junction between adjacent blocks was substantially 12 volt. At higher ten'iperatures higher voltages may be maintained between the resistor portion. Howlver, the voltage drop across each junction and the voltage across the entire divisfon is preferably maintained at as low a magnitude as possible in order to prevent pos-sible arcing between the resistor portions and. in general to give the best operating results. At the end ot the tive weeks run, no visible deterioration of the resistor portions was noted. Preferably, during the operation ot my heating unit the voltage of the energy supply is maintained substantially constant. lt has been found, however, that commercial sources ot electric energy have been satisfactory from this standpoint, the device itself compensating for any normal variation in the applied voltage. This feature will be understood from the consideration that a minor change in the voltage of the source of energy to which the heating unit is connected will be partially compensated for bv the inherent operation of the resistor. A slight decrease in the applied voltage causes the cuii'rent flowing through the resistor to decrease and this causes a slight cooling of the resistance unit. rllhe cooling ot the resistance unit decreases the resistance as pre viously explained and thereby causes an increased current to flow.

ln Figs. l5 and 16 is shown a form of heating units in which a series oi spirally aligned resistor blocks 70 are disposedy in cooperative relation with a spiral cooperating member 71. Between the base 72, and the blocks and members 71 is disposed electrical insulation 73. Between the blocks 70 and the spiral member 71 is disposed electrical insulation (not shown). The inner end of the spiral member 71 is fastened to but insulated from the conducting block 74. The outer end of the spiral member 71 is connected to but insulated from the fixed conducting block 75. Conductor 76 is connected to the block 74, and conductor 77 to the block 75. Movable through the block is the threaded spindle 78 provided with a knurled head 79 at one end and connected at the other end through a suitable joint to the block 80. By turning the head 79 a predetermined longitudinal pressure may be applied to the spirally aligned blocks 70. The blocks 70 are shown as having one end of cylindrical concave shape and the other end of cylindrical convex shape. whereby adjacent blocks may readily contact with each other whatever the curvature of the spiral.

In Figs. 11 and 12 is shown a spiral form of heating unit in which spirally aligned resistor blocks 81 are disposed between the iixed blocks 82 and 83, adjustable pressure on the resistor blocks being obtained by moving a spiral cooperating member 84. The member 84 is fixed at its inner end to the block 82 but insulated therefrom. The outer end or' the member 84 is aHiXed to the spindle 85. The resistor blocks 81 are shown as cylindrically convex at one end and cylindrically concave at the other end, whereby said resistor blocks may readily contact one with another regardless of the curvature ot the spiral. Connected to the conducting block 82 is the electric conductor 86, and connected to vthe conducting block 83 is the conductor 87. The blocks 81 and member 84 are electrically insulated from the base 88 by insulation 89. The blocks 81 are insulated from the member 84 b y suitable insulation (not shown). Mounted on the base 88 is a member 90 through which is movable a threaded spindle 85, which is provided with a head 91 at one end, and to the other end of which is attached the spiral member 84. By turning the head 91, the length of the spiral 84 between the stationary blocks 82 and 88 may be shortened to thereby impose a predetermined pressure upon the aligned blocks 81.

In Figs. 5 and 6 is shown a modiiied form of heating unit in which a plurality of resistor particles or bodies are employed. The resistor particles 92, which may be of any suitable shape, are shown as confined within a closed tube 11. The end 13 may be suitable aiiixed to the tube 11 by any suitable means, as by welding. The blocks 14 and 15 are shown as similar to the corresponding blocks 14 and 15 in Fig. 3. Insulating means 3, conductors 4 and 5, spindle 8, boss 9 and handle 10 are similar in construction and 'function to the corresponding members described under Figs. 1 and 2. Initial pressure is imposed on the resistor particles 92 by turning the lrnurled head 10, and thereby causing the block 15 to move toward the block 14.

The resistor blocks adapted to be employed in heating units of my invention may be of various shapes, several forms of which have been discussed in the above description. In Fig. 21 is shown a resistor block 100 of trapezoidal cross-section, such as might be employed in the form of heater unit shown in Fig. 9, although a rectangular form of resistor block 101, as shown in Fig. 23, may also be employed in the heater shown in Fig. 9. The block 101 is of substantially the same shape as that shown in Fig. 1. In Fig. 22 is shown a cylindrical form of resistor block 102 substantially similar to that shown in the heater in Fig. 3. In Fig. 24 is shown a. resistor block 93, which may be satisfactorily employed in spiral heater units such as shown in Figs. 11 and 15. The ends of the block 93 are both shown as eylindrically convex, whereby said block may uniformly contact with adjacent resistor blocks regardless ot' the curvature in a spiral form of heating unit. The resistor block 103 shown in Fig. 25 is provided with one end of cylindrical concave form and the other end of cylindrical convex form, whereby the block may be readily employed in a curved or spiral form of heater, such as, for example, the heater shown in Fig. 15. An apertured spherical form of resistor block 49 is shown in Fig. 2G, which is substantially similar to the resistor block employed in the heater shown in Fig. 19. The cylindrical resistor block 104 shown in Fig. 27 is provided with one spherical concave end and one spherical convex end, whereby electrical contact may readily be obtained between the adjacent blocks when employed in a curved or spiral heater. The cylindrical resistor block 94, as shown in Fig. 28, is provided with spherically convex ends and shows in an enlarged form substantially the Same form of resistor block shown in Figs. 18 and 14. Resistor` blocks provided with curved ends, such as above described, may also be employed, of course, in straight forms of heaters. In Fig. 29 are shown various forms of resistor particles adapted for use in a form of heating unit such as shown in Figs. 5 and 6. The particles 95 are represented as being of irregular shape. However, it may be desired in a heating unit such as shown in Figs. 5 and 6 to employ particles of uniform shape and size. In such case, spherical particles 96 or rectangular particles 97 may be employed.

ln Fig. 3() is shown a resistor block 98 provided with an insulating shell 99 which may be of any suitable material, having preferably the same temperature coefficient of eX- pansion as the resistor material. Thus, with a resistor block such as oitl graphite there may be employed an insulating shell composed of material such as porcelain or alundum. lf a block 9S were employed in a heating unit such as shown in Figs. 13 or 17, other insulation would be unnecessary between the resistor blocks and the walls of the spiral cavity of the heater.

The operation oft a. heating unit contemplated by my invention may be understood by reference to the construction shown in Figs. 1 and 2. The resistor blocks or bodies 2 are placed under a certain predetermined initial longitudinal pressure between the conducting blocks 6 and 7. The longitudinal pressure through the series ot' resistor blocks is, of course, exerted in the direction of passage oit the current through the blocks, regardless of whether the series ot blocks is arranged in straight or curved alignment. The higher the operating temperature desired the greater is the initial pressure imparted to the series ot resistor blocks. By connecting the conductors t and 5 to a suitable source of alternating or direct current, electric energy, preferably at a. constant voltage, is passed through the series of resistor blocks 2. Heat is developed from said electric energy, due in part to the resistance ot' each block 2 and in part to the contact resistance between adjacent resistor blocks. A portion of the heat genera-ted is transmitted to the container or expansion member 1, which has a relatively large temperature coefficient ot' expansion with respect to that of the resistor blocks.

The temliiera-ture oi the heating unit rises tothe predetermined temperature, the current meanwhile constantly din'iinishing at which predetermined temperature the heat generated within the. heating unit is equal to the heat dissipated thereby. Thus. considering the operation ot the unit when the desired temperature has been reached, further increase in ten'iperature of the container 1 decreases the pressure between adjacent resistor blocks and thereby greatly increases the resistance of the series, thus reducing the current and consequently the heat developed. The container 1 is thereby slightly cooled and contracts, thereby appreciably increasing the pressure between adjacentl resistor blocks and hence decreasing` the resistance of the series. The current is thus increased and also the rate of d-evelopmcnt ot heat, whereby the container 1 is slightly increased in temperature. The above cycle continues during the operation of the heating unit. hus it will be seen that my heating unit has very high temperature coeiticient of resistance, greater than that ot any known metallic resistor, as a result ot which substantially constant temperatures may be maintained with variations ot butI very small magnitude.

lt may be noted that other things being equal, the sensitivity of the heating unit, namely, the closeness of temperature control thereof is proportionate to the distance between the junctions ot the resistor portions. Thus, where the resistor blocks are relatively long, the length of the cooperating member is proportionately increased and hence a smaller increase ot temperature is necessary to decrease the pressure between adjacent resistor blocks. Thus, the degree ot sensitivity desired in a heating unit may be controlled by the size ot resisto-r portions employed, and it it be desired to have the temperature range relatively large this can be secured by using` a. larger number ot resistor blocks per unit ot' length ot the heating unit.

.lt will thus be noted that my device maintains a` substantially constant temperature with the desired degree ot' sensitivity, which may be varied, for example, by the size and number ot' resistor blocks, as previously set forth.

Resistor blocks and resistor particles employed in heating units contemplated by my invention may be ot' any suitable material, preferably of high resistance. Various forms of carbon, including compressed graphite, have been found satisfactory for this purpose. Graphite is particularly advantageous due to its low coefficient of thermal expansion. Although carbon has a negative temperature coefficient of resistance, my invention is not confined to th(` use ot resistor portions ot this character. Tn general` resistor blocks of as high resistance as possible are desirable, as thereby the number ot resistor blocks which must be employed in a heating unitl for use with electric energy oli a given voltage may be greatly reduced.

The cooperating member, support or container employed in heating units embodying my invention have preferably a very high temperature coefiicient ot expansion with respect to that of the resist-or material. Thus iron, copper. brass, aluminum and metals of similar character are very desirable t'or such use.

The resistor material may be electrically insulated from the container or cooperating member by any suitable means. For example, the cooperating member may be vitreous enameled. This method is` very satisfactory, particularly for ferrous members. Mica mightalso be employed as insulating material. Furthermore, resistor blocks may themselves be provided with an insulating coating such as shown in Fig. 31.

Such resistor blocks ai'e advantageous Where the cooperating member is or a material not readily viti'eous enameled, such as, for eX- ainple, copper, brass or aluminum.

It will thus be seen that l have pi'ovided a heating unit which is adapted to maintain itseli automatically at substantially constant temperatures.

It will further be noted that l have provided a heating unit o't i'elativcly simple and substantial construction and ot very high temperature coellicient oit resistance.

it ivill inoi'eovei' be seen that I have pi'ovided an elccti'ical heating unit Which will vei'y rapidly heat up to a predetermined desired ope 'ating' temperature and which ivill maintain itselt' at the operating temperature ivith the desired sensitivity.

Furthermore. it is to be understood that the particular forms ot apparatus shown and described, and the particular' procedure se-t forth, are presented for purposes ot explanation and illustration and that various modifications oit said apparatus and procedure can bei made Without departing trom my invention as dehiied in the appendtal. claims.

lVhat l claim is:

1. In an electrical heating unit adapted to maintain substantially constant temperatures, in combination, a plurality ot electrically conductive resistor bodies, confining means disposed in electrical insulating and heat receiving relation to said resistor' bodies and adapted to place said bodies under a predetermined initial pressure, said contining means being adapted to vary the pressure betiveen said resistor bodies inverselyT With the variation in temperature of said coiitining' means.

2. ln an electrical heating unit adapted to maintain substantially constant temperatures, in combination, a plurality ot electrically conductive resistor bodies, means ot relatively7 high temperature coetticient ot expansion confining said resistor bodies, and means tor passing current through said resistor bodies, whereby said bodies may be heated and may maintain said contining means at substantially constant predetermined temperatures.

3. In an electrical heating unit adapted to maintain substantially constant temperatures, in combination, a plura ity of electrically conductive resistor bodies, a confining means ot relative y high teinperature coctticient ot expansion adapted to confine said resistor bodies and to receive heat therefrom, means associated with said confining means to apply a predetermined pressure to said resistor bodies, and means for 'passing electric current through said resistor bodies, ivliei'eby said bodies may be heated to maintain said conlining' means at substantially constant predetermined temperatures.

fl. An electrical healing unit comprising a plurality ot substantially aligned electrically conductive i'esistoi' portions, a coniining means disposed in electrically insulating and heat receiving relation to said rcsistor portions and adapted to place said portions under a predetermined initial pressure and to maintain said portions in aligned relation, adjustable means to vary said initial pi'essure, and means itor passing current through said resistor portions.

5. An electrical heating unit con'iprising a plurality ot substantially aligned electrifally conductive resistor blocks, a coiilining means adapted to place said blocks in aligned relation under a predetermined initial pressure, adjustable means to vr'ary said initial pressure, and means 'loi' passing' cui'- rent through said resistor blocks, whereby said confining' means may be maintained at substantially constant pi'edetei'miiicd ltenipei'atures.

(i. In an electric heating unitadapted to maintain itseli'f at substantially constant temperatures, in combination, a. series ot substantially contacting aligned resistor blocks, a member having a relatively high temperature coetiicientot expansion with respect to that of said blocks disposed iii cooperative relation to said blocks and adapted to receive heat therefrom, means for electrically insulating said member from said blocks, means toi' supplying electric energy to said aligned blocks, and means for placing said blocks under a predetermined initial longitudinal pressure variable ivitli the expansion and contraction ot said member' due to heat received trom said resistor blocks.

7. In an electric heating unit adapted to maintain itself at substantially constant temperatures, in combination, a series olf substantially contacting aligned resistor blocks, a support for said blocks having a relatively high temperature coefficient ot expansion with respect to that ot said blocks, said support being adapted to receive heat from said blocks, electrical insulating means disposed betiveen the electrically conductive portions of said blocks and said support, electrical conductors connected to the ends oii said sei'ies of blocks whereby electric cui'- rent may be passed through said blocks, and cooperative means acting on the ends ot said series oit blocks adapted to place said blocks under a predetermined initial longitudinal pressure variable ivith the expansion and contraction ot said support due to heat received from said resistor blocks.

8. ln an electric heating unit adapted to electrical insulatingl relation to said blocks, lsaid support being adapted to receive heat trom said blocks, electrical conductors conneeted to the ends of said series of blocks whereby electric current may be passed through said blocks, a member disposed at one end of said series of blocks cooperating with an adjacent portion of said support to form a stop for further movement of said blocks towards said member, and adjustable means disposed adjacent the other end of said series of blocks, cooperating with an adjacent portion of said support and adapted to apply a predetermined initial longitudinal pressure to said blocks variable With the expansion and contraction of said support due to heat received from said resistor blocks.

9. ln an electric heating unit adapted to maintain itself at substantially constant temperatures, in combination, a series of substantially contacting spirally aligned resistor blocks, a container comprising a pair of cooperating` metal members adapted to substantially enclose said blocks and maintainv said blocks in said spirally aligned relation and having a relatively high temperature cocllicient of expansion with respect to that of said blocks, electrical insulating means disposed between the electrically conductive portions of said blocks and said support, electrical conductors connected to the ends of said series of blocks whereby electric current may be passed through said blocks, a member-disposed at one end of said series of blocks cooperating with an adjacent portion of said support to form a stop for further movement of said blocks towards said member, and adjustable means disposed adjacent the other end of said series of blocks cooperating with an adjacent portion of said support and adapted to apply a prcdetermined initial longitudinal pressure to said blocks variable with the expansion and contraction of said support due to heat received from said resistor blocks.

i0. ln an electric heater unit adapted to maintain itself at substantially constant tempcratures, in combination, a container of relatively high temperature coefficient of eX- pansioif, a plurality of resistor particles of relatively low temperature coet'iicicnt of eX- pansion as compared with that of said container disposed in substantially contacting relation and in close conlinement Within said container, said container being adapted to receive heat from said resistor particles, electrical insulating means disposed between said particles and said container, electrical conductors disposed adjacent to said resistor particles whereby electric current may be passed through said particles, and cooperative means adapted to place said particles under a predetermined pressure variable with the expansion and contraction of said container due to heat received from said resistor particles.

ll. In an electric heating unit adapted to maintain itself at substantially constant temperatures, in combination, a series of substantially contacting aligned carbonaccous resistor blocks, a metal container for said blocks adapted to maintain said blocks in said aligned relation and having a relatively high ternperature coelticient of expansion with respect to that of said blocks, said container being adapted to receive heat from said blocks, electrical insulating means disposed between the electrically conductive portions of said blocks and said container, electrical conductors connected to the ends of said series or' blocks whereby electric current may be passed through said blocks, and cooperative means acting on the ends of said series of blocks adapted to place said blocks under a predetermined initial longitudinal pressure. variable with the expansion and contraction of said container due to heat vsreceived from said resistor blocks.

"\12. In an electric heating unit adapted to *maintain itself at substantially constant temperatures, in combination, a series of re sist-or blocks having curved ends, at least one end of each block being convexly curved, said blocks being arranged in substantially contacting curved alignment, a support for said blocks having a relatively high temperature coetlicient of expansion with respect to that of said blocks, said support being adapted to receive heat from said blocks, electrical insulation disposed on said blocks adjacent said support, whereby said support is electrically insulated from said blocks, electrical conductors connected to the ends of said series of blocks whereby electric current may be passed through said blocks, and cooperative means acting on the ends of said series of blocks adapted to place said blocks under a predetermined initial longitudinal pressure variable with the expansion and contraction of said support due to heatreceived from said resistor blocks.

13. In an electric heating unit, in combination, a series of aligned graphite resistor blocks, an expansion member cooperating with said blocks along the linear extent thereof and arranged to receive heat therefrom and having a relatively high temperature coefficient of expansion with respect to that of said blocks, electrical insulating means disposed between said graphite blocks and said expansion member, means for passing electric current through said series of blocks to heat said blocks, and means to place said blocks under a predetermined initial pressure longitudinally of said series of blocks variable with the expansion and contraction of said expansion member due to heat received from said resistor blocks.

14. In an electrical heating unit, in combination, a substantially curved expansion member, a series ol aligned resistor blocks disposed closely adjacent said expansion member on the concave side thereof and closely 'following the concave curvature thereof, said expansion member having a relatively high temperature coefficient of eX- pansion with respect to that of said blocks and being arranged to receive heat from said blocks, said blocks being electrically insulated from said expansion member, means for placing said blocks under a predetermined initial pressure longitudinally of said series of blocks, whereby a component of said longitudinal pressure presses said blocks against said expansion member` with a force proportional to said longitudinal prcssiiirc., said longitudinal pressure being variable with the expansion and contraction oi' said expansion member due to heat received from said resistor blocks, and means for passing electric current through said series of blocks to heat said blocks.

In testimony whereof I aiix my signature.

STERNE MORSE. 

